The present invention relates to an electro/optical combined type network node control system for use in a transport network with electrical paths and optical paths.
Recent advance in optical fiber transmission technologies has further improved the transmission bandwidth. Coupled with this improvement, development of a high-speed broadband transmission network has been anticipated that provides integrated communication services for audio, text, and/or image data. A transfer network technology is one of the essential factors for the realization of the high-speed broadband transmission network. The transfer network is in a hierarchical form of a line (channel) layer, a path layer, and a transmission path medium layer, as described in Ishikawa, "A New Concept for Telecommunications Network Architecture", NTT R & D, Vol. 38, No. 4, 1989, pp. 395-408 (1989). Typical switching systems switch a connection established between end users. The connections between the switch systems are combined into a path. Therefore, the connections are switched by path in a cross-connecting unit placed between the switch systems and re-directed towards the destination. The data are thus transferred between the switch systems.
The path layer, which is the "brain" of the transfer network, uses layered paths based on new synchronous digital hierarchy (SDH) in a synchronous transfer mode (STM). In addition, the path layer also employs a virtual path supporting an asynchronous transfer mode (ATM). The path supporting the SDH/ATM is generally referred to as an electrical path.
A conventional transport network using a virtual path is described in, for example, Yoshio Kajiyama et al., "An ATM VP-based Self-healing Ring", IEEE Journal on Selected Areas in Communications, vol. 12, No. 1, pp. 171-178 (January 1994). A transport network system using the above-mentioned virtual paths consists of a plurality of network nodes. For the transport network system consisting of first through third network nodes, each network node has a virtual path switch. A network node is connected to an adjacent network node via a bi-directional transmission path. A first bi-directional virtual path is transferred between the first and second network nodes. A second bi-directional virtual path is transferred between the first and third network nodes through the second network node. The first through third network nodes are further connected to a different (or remote) network such as an area network, a subscriber's access network, and a local area network. The virtual path extending from the first network node to the different network is switched with different other network nodes. In contrast, the virtual path from the different network nodes is switched with a different network connected to the first network node. For the switching of the virtual path from the first network node to the third network node, no switching is made in the second network node located between the first and third network nodes.
A detailed configuration/architecture of the above-mentioned network nodes and the virtual path switches is described in, for example, Yoshio Kajiyama et al., "An ATM VP-based Self-healing Ring", IEEE Journal on Selected Areas in Communications, vol. 12, No. 1, pp. 171-178 (January 1994), and Ryutaro Kawamura et al., "Self-healing ATM Networks Based on Virtual Path Concept", IEEE Journal on Selected Areas in Communications, vol. 12, No. 1, pp. 120-127 (January 1994). According to these articles, the network node is referred to as a cross-connecting unit or an add/drop multiplexer (ADM).
The transport network system with the above-mentioned virtual path either switches the virtual path from the network connected to the local network node to any one of different network nodes, or switches the virtual path from the different or remote network node to the network connected to the local network node. No switching is made in the network node between the local network node and the other network node. This allows elimination of one-by-one switching of the virtual channels in the virtual path.
The introduction of an optical path, in combination with the electrical path based on the above-mentioned electrical transmission switch technique, has been examined to improve transmission capacity of the transport network. An example of the transport network using such an optical path is supposed in, for example, Ken-ichi Sato et al., "Network Performance and Enhancement with Optical Path Layer Technologies", IEEE Journal on Selected Areas in Communications, vol. 12, No. 1, pp. 159-170 (January 1994).
For the transport network consisting of first through fourth network nodes using the above-mentioned optical paths, each network node has a virtual path switch and an optical path switch. A network node is connected to an adjacent network node via a bi-directional transmission path. A first bi-directional optical path is established between the first and second network nodes. A second bi-directional optical path is established between the first and third network nodes. A third bi-directional optical path is established between the first and fourth network nodes. The first through third bi-directional virtual paths are multiplexed into the first through third optical paths, respectively, and are switched from one network node to the other via the network nodes.
Each network node "maps" the virtual and optical paths. More specifically, the virtual path switch in the first network node multiplexes/demultiplexes the first virtual path for the first optical path, multiplexes/demultiplexes the second virtual path for the second optical path, and multiplexes/demultiplexes the third virtual path for the third optical path. Likewise, the virtual path switch in the second network node multiplexes/demultiplexes the first virtual path for the first optical path. The virtual path switch in the third network node multiplexes/demultiplexes the second virtual path for the second optical path. The virtual path switch in the third network node multiplexes/demultiplexes the second virtual path for the second optical path. The virtual path switch in the fourth network node multiplexes/demultiplexes the third virtual path for the third optical path.
The second network node switches the second and third optical paths from the adjacent first and third network nodes to the third and first network nodes, respectively, by means of the local optical path switch. Likewise, the third network node switches the third optical paths from the adjacent second and fourth network nodes to the fourth and second network nodes, respectively, by means of the local optical path switch.
A detailed configuration architecture of the above-mentioned network nodes and the optical path switches is described in, for example, Atsushi Watanabe, Satoru Okamoto, and Ken-ichi Sato, "Optical Path Cross-Connect Node Architecture offering High Modularity for Virtual Wavelength Path", IEICE Trans. Commun. Vol. E78-B, No. 5, pp. 686-693 (May 1995), and Atsushi Watanabe, Satoru Okamoto, and Ken-ichi Sato, "Optical Path Cross-Connect Node Architecture with High Modularity for Photonic Transport Networks", IEICE Trans. Commun. Vol. E77-B, No. 10, pp. 1220-1229 (October 1994).
Each optical path corresponds to an optical wavelength signal in conventional transport networks involved in a wavelength division multiplexing and a certain wavelength may be selected for a single optical path. Alternatively, the certain wavelength is selected for each connection between the network nodes and the signal on that wavelength is switched in a trunk network node. In any cases, routing and switching technique for the optical wavelengths are still under development. These techniques require no complicated header processing such as cell switching achieved in an ATM virtual path switch and is based on a simple principle. Accordingly, they are expected to find wide variety of applications to a high speed, large capacity switch system.
The transport network system using the above-mentioned optical path multiplexes a plurality of electrical paths into a single optical path that are directed to the same destination. The network node located on the optical path switches the optical path without changing it into an electrical signal. Thus, the network nodes are directly connected to each other by means of the optical path. This reduces a load on the electrical path switch for switching.
Traffic characteristics of the virtual path vary or fluctuate successively. However, an optical path is fixedly allocated to the electrical paths directed to the same destination. Therefore, a plurality of optical paths and, in turn, different wavelengths are required to establish the optical paths between certain network nodes.